The present invention relates to a safety clasp which may be used more particularly but non-exclusively for articles of jewellery, such as necklace chains, bracelets, etc . . . .
Among the various types of clasps for necklace chains existing at present, certain types comprise two pieces sliding in each other, namely an outer sleeve at one end of which is hooked an end link of a necklace chain, and an inner slide element of which the relative movement with respect to the outer sleeve makes it possible to engage the other end link of the chain in this slide element. Certain clasps of this type, such as those described in U.S. Pat. No. 3,984,900, comprise, in that part of the outer sleeve which is opposite the part where the first link of the chain is hooked, a slot for introduction of the second end link of the chain, this slot being substantially in the form of an L of which one arm, extending transversely, opens out through an access opening in the wall of the sleeve and of which the other arm extends longitudinally. The slide element presents a notch opening out transversely and adapted to be brought opposite the transverse arm of the slot, to enable the second link of the chain to be engaged in this slot and this notch and then make it possible to pull, via this link, on the slide element to bring the second link in the bottom of the longitudinal arm of the slot.
Although such a clasp makes it possible easily to engage and disengage the second link of the chain, i.e. the one which is not permanently connected to the outer sleeve, it nonetheless presents the drawback of opening unexpectedly since the inner slide element can move freely inside the outer sleeve.
Another type of known clasp is described, for example, in French Pat. No. 2 270 820. This clasp comprises a slide element which may be locked in the outer sleeve, in position of closure, by means of a tooth engaging in a hole provided in the wall of the sleeve. However, when the clasp is closed, the slide element projects outside the outer sleeve, in the longitudinal direction, and at that spot it presents an opening in which is engaged the second link of the chain. Such a clasp presents the drawback of opening easily if the chain is pulled upon, the end part of the slide element projecting outside the sleeve being easily deformed. Furthermore, it is not easy to open the clasp since, in order to be able to bring the slide element completely out of the sleeve, it is necessary to push the tooth previously, using one's nail, for example, for it to leave the hole in the sleeve.